Senate lawmakers have opened the door to a fight over military-funded abortions, voting in committee to expand abortion coverage for servicewomen to cases of rape or incest as part of a major military spending bill expected to hit the chamber next month.

Democrats have tried in the past to overturn the 16-year-old ban on military funding for abortion except when the mother’s life is at stake, but the latest attempt picked up some bipartisan traction last week in the Armed Services Committee, with GOP Sens. John McCain, Susan M. Collins and Scott P. Brown signing on.

While pro-life groups oppose expanding the exemptions, it’s a grayer area for some Republicans who point out that it mirrors the Hyde Amendment — the law that has for decades limited taxpayer dollars to be used only for abortions in the cases of rape, incest or to save the life of the mother.

Sponsored by Sen. Jeanne Shaheen, New Hampshire Democrat, the amendment would allow the Department of Defense to pay for abortions in all three circumstances. Right now, women who are pregnant due to rape or incest can only get an abortion at military hospitals if they pay for it themselves.

Undergirding the debate are heightening concerns about rising rates of sexual assault in the military. Supporters of the legislation say it’s unfair that women who work in other sectors of the government can get coverage for abortions if they are raped, but that doesn’t extend to military members and their families.

“This is about equity,” said Mrs. Shaheen, after the Senate committee passed her legislation 16-10 on Thursday. “Civilian women who depend on the federal government for health insurance — whether they are postal workers or Medicaid recipients — have the right to access affordable abortion care if they are sexually assaulted.”

But pro-life advocates insist that expanding coverage for abortion isn’t the answer, saying it takes the focus off preventing the assault in the first place.

“One of the things the Democrats use is the high number of assaults in the military,” said Shari Rendall, director of legislation for Concerned Women for America. “Why not focus that attention on preventing the rape and assault instead of killing a baby, which is a result of the unlawful assault on a woman?”

She offered two amendments last year that were blocked on the Senate floor; one contained the rape and incest provision, while the other would have allowed made elective abortions available at military medical centers if paid for out of pocket.

Narrowing her focus this time around may have helped win some GOP votes, but the amendment faces an uncertain future. Even if the Senate includes it in its final defense bill, anything could happen when lawmakers meet to hammer out differences between the House and Senate versions.

House Republicans are likely to mount a strong resistance, backed up by leading pro-life groups such as National Right to Life, Americans United for Life, Concerned Women for America and SBA List, all of whom oppose expanding the restrictions.

But a spokesman for Mr. McCain said his boss is simply voting for the same abortion funding restrictions he’s supported in the past.

There have been a handful of attempts to overturn the existing ban ever since the Republican-controlled Congress passed it in 1996 and President Clinton signed it into law.

The Senate passed a measure in 2004 with the rape and incest provisions, but it failed to pass the House. In 2010, Republicans rebuffed an amendment offered by Illinois Democratic Sen. Roland Burris to lift the ban on privately-funded abortions.

And last year, a group of House and Senate Democrats introduced the legislation nearly identical to the amendments Mrs. Shaheen offered. The DOD announced that it supported the bill, saying it would make the military rules more consistent with other major abortion-funding restrictions in federal law.

This year, pro-life leaders say they’re surprised that Mr. McCain voted to tack the Shaheen amendment onto the defense bill, warning an abortion fight could jeopardize legislation essential to funding the U.S. military.

“It’s a little surprising to see Sen. McCain voting for it, because it opens the door to all these further complications on the underlying bill, which I think he would want to avoid,” Douglas Johnson, legislative director of the National Right to Life Committee.